Makes like a chewing sound, as you press the up button it may be possible to "pull" the glass up a bit at a time, I managed this when mine went.
If you search on a my posts you should find a fairly detailed explination of how to get this regulator out, not a very hard job really, not as hard as you think. your main worry at present is your car in insecure and when you drop the roof the next time it may pull that rear window down a bit, it also drops as you drive it so if you get it up tape it in place with electric tape.
mine is still broken, I have an 07 reg in my garage which I will fit soon. I sugest you do the same at present as it makes the car secure again, to do this.
Find and follow my explination on removal. Once you get the reg out remove the cables from the motor completly easy to do and self explanitary when you see it, but you need to get rid of them as you will still be using the motor once cables are out, you need to push the window on its guides to the top of its travel and use two nuts and bolts through the 2 guide slots with washers directly under the metal glass holder tighten the bolts up these hold the window glass up again once out and in your hand self explanitary, replace reg and make sure you conect the motor up as well bolt it all in place do not put the trims back instead take out the 3 large rubber gromets on the rear panel one is by a haydraulic ram for the roof can't miss em pop em out, put up roof close front door, when roof is goinf on watch the rear glass to see what happens as you don't want the glass to high as it will make the roof leak, you will possibly find the glass is not quite right sitting wise so you can adjust the rear glass through these large rubber gromet holes with a 10 mm socket Slacken the bolts a bit, DO NOT OVER TIGHTEN THEM!!!!!! you may shatter the glass, you can tilt it, drop and rasie is a bit on these mounts to get a good seal. You need the front door shut with window up to align it all.
once this is done, drop roof again and reassemble trims - Job Done takes me about 1 hour to do job start to finish.1st time it took around 2 hrs as took time to be sure so allow around 2/2.5 hrs first time around.
Roof works fine, window does not go down but motor turns, not sure you see if the roof reads the motor turning so I just conected it with out the cables.
Once Cables have chewed up motor is usually ok but the mechanism inside will be US as it is plastic and all the small tracks on the winder are ruined, if you get a motor for it (ebay) you must replace the cables as well (not avalible, unless you have them specially made again window cables -ebay) any kink in the winding cables will destroy the motor mechanism very quickly. looks a bit of a pain to rewind the cables - should make for a few hours of total swearing and flustration at the fact you only have two hands but really need 3.
BEST BET!
New reg comes with its base palate, motor and cables but no glass price in around £195.00 + VAT I belive from Renault
EBAY! excellent source of parts - Will not be listed, so you need to search for scrapping megane CC, or just scrapping megane scroll till you find a few CC's and use the ask seller a question button, same goes for anyone selling CC parts, just ask, this is what I do when I need anything for it you will be suprised what people have but don't list - hand brake is a great one listed one went for £105 I was after it but left it after £80, did the above asked about a H/Brake and bought one for £35 from a scrap dealer, got my Rear Reg the same way for £85 as it was from an 07 car, the 05 reg I used earlier which broke (my fault as didn't adjust it and it kept hitting the roof) cost £55 so they are around if you keep looking and the bolt idea extends you time frame with out costing you roof down time, both used regs came on there base plates with motor and cables no glass same as you would get from Renault, Watch out for the Megane Phase 1 regs for the cabs they look almost the same but they don't fit, do NOT buy a 5 door rear reg it is not the same a lot of things do cross some don't this rear reg is one of them. (the hand brakes do and are a lot cheaper from a hatch or est or saloon than a CC)
Hope this helps.
Sorry mate. I meant driver side front window... sorry. Is there a way to lift if about 5mm up so that it seals properly. 
Roll on Summer!!